Forming Plexiglas / acrylic

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BJC

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I need to form a compound curve in small piece of acrylic to make a flush landing light lens in the cowling. The circular lens is about 1/8" thick and 5" in diameter. It will need to have a concave shape about 3/4", but it is not symmetric.

I know the process for heating a sheet in an oven, and stretching it over a form (of vacuuming it into a form), but I have no experience doing it.

Two questions:

Can it be carefully heated with a calibrated heat gun, and free formed over the fiberglass cowl?

If not, what tips do you have for the oven process?

Thanks,

BJC
 
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Mcmark

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Byron,
I helped a neighbor who was in the acrylic business, build and install the acrylic on the Mercury capsule at Air and Space.
I won't say I know a lot, but what I've seen, a heat gun, makes it very difficult to get the heat even on the acrylic. For a 5" piece I'd give it a shot, but i think I'd try using an oven. You could use a toaster oven for that small a piece. The thing is, they always warm the parts in the vertical plane. Use a frame to support the sheet on at least the top, best to use 4 corners.
He used compressed air to force the shape (blow) but also to cool an area to not allow that part to change any further. I've drape formed some things over a buck, if you will. That might be your best option. Use Pink or Blue foam to get your shape, seal it with epoxy or glass, add a good quality felt over and drape it. Cut to shape, cause you leave it big to handle on the edges.
Just my $.02
Mark
 

kent Ashton

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You might make a form out of whatever is handy and a "stretcher" that pulls the acrylic down over the form. I have used a piece of 3/4" plywood with a hole larger than the form. Heat the plexi in an oven until somewhat floppy and quickly stretch it over the form. The form needs to be nice or it will imprint on the inside of the plexi. Maybe try a flannel liner over the form
 
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BBerson

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Small piece doesn't need to hang vertical. We did hand formed windshields using a flat oven.
Try 275° first. If not hot enough go to 325°. Soak in oven 15 minutes. Heat lamp might work.
 
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plncraze

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Jim Marske emphasized using cast acrylic when doing molding. Tony Bingelis had a couple "Sportplane Builder" articles on forming his Falcon wing tip lenses.
 
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wsimpso1

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Byron,

Funny you are doing this now. I am getting ready for wing tip lenses right now. I keep hearing the same advice. I am going for stretch forming. I have the bucks, building a vacuum box, just bought a yard of fleece that is springy enough (I hope) to go over the buck without wrinkles, a frame made, and have to figure out just how I will heat a 12" by 24" piece of Plexi... probably buy a cheap infra red heater. Yours sounds easier..., I am doing this because I need to figure out how to do it for my windshield and windows.

Billski
 
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blane.c

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You can get used ranges from craigslist and other for practically nothing in fact sometimes literally for nothing. Has Thermostat control. Because you don't care about it aesthetically you can take the tin snips to the side or back and with the addition of some extra sheet metal voila' it is like magic exactly the size you need. For something I am thinking about I will use two of them side by side separated by a short distance but with a sheet metal "tunnel" connecting, I have them both and both are convective (with fans inside to move air).
 
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Pops

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Local man made a 4'x4' x8' steel oven with a mono-rail on top to put things in the oven for power coating. Made from 11 gauge steel with 6" of fiberglass insulation on the outside then covered with sheet steel roofing . Several electric stove heating elements and thermostats. Worked very good for his power coating business. Had him power coat my rudder pedals, stick assembly and flap handle and engine valve cover pans on the JMR when he had the oven heated up for a large job. Small version would work for forming windshields, etc.
 
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